Heretofore, it has been known that, when a living body is irradiated with light, photoacoustic waves (typically, ultrasonic waves) are produced due to an increase in temperature and thermal expansion of the tissues of the living body which are caused by optical absorption of the living body. Attempts have been made to apply photoacoustic imaging, in which the inside of a living body is visualized in a non-invasive manner by using photoacoustic signals which are received signals of the photoacoustic waves, to clinical practice. The definition of the lower limit of the frequency band of an ultrasonic wave is not always definite. However, an elastic wave of 20 kHz or more is herein called “an ultrasonic wave”.
In addition, it has been expected that diagnostic accuracy in clinical practice can be markedly increased by combining photoacoustic imaging with ultrasonic imaging in which an ultrasonic image is generated by using ultrasonic signals which are received signals of the reflected waves of ultrasonic waves transmitted to a specimen.
As a probe with which photoacoustic imaging and ultrasonic imaging can be combined as described above, a probe has been proposed in which a transducer array for receiving photoacoustic waves and a transducer array for transmitting/receiving ultrasonic waves are arranged in parallel (see PTL 1).